Coating compositions comprising binders having alkoxysilane groups have been known for a long time. In the presence of atmospheric moisture, the alkoxysilane groups of the binders are capable even at room temperature of undergoing condensation with elimination of the alkoxy groups to form Si—O—Si bridges. Coating compositions of this kind are suitable, for example, for producing automotive refinishes. In that context, they have a critical advantage over the more often used isocyanate-based coating compositions in that they are significantly less objectionable from a toxicological standpoint, permitting their application largely without the extensive precautionary measures that are necessary with isocyanate-based coating systems.
Hoffmann et al., WO 2010/112106, incorporated herein by reference, discloses moisture curing coating compositions based on aprotic solvents comprising (A) at least one binder having alkoxysilane groups and (B) at least one phosphorous- and nitrogen-containing crosslinking catalyst. The binder (A) is combined with organic solvent and other desired coating ingredients, and the catalyst (B) is admixed into this coating material just before use. The binder comprises at least one polyacrylate and/or polymethacrylate which is obtainable using one or more ethylenically unsaturated monomers (a1) of the formula (I)
in which R is H or methyl, R′ is H, alkyl, or cycloalkyl, R″ is alkyl, cycloalkyl, aryl, or aralkyl, and x=0 to 2. The coating compositions of WO 2010/112106 exhibit rapid curing in the presence of moisture to be tack-free after curing at 60° C. for just 30 minutes and also have a potlife of at least 30 minutes, specifically of at least 2 hours. WO 2010/112106 also discloses that at least proportional use of acrylate- and/or methacrylate-functional alkoxysilanes with ethoxy groups instead of methoxy groups to prepare the binders provides coating compositions that, on curing, release very little methanol and that, nevertheless, exhibit the requisite rapid curing.
Typically, the reactive components of an ambient-cured, thermosetting coating are kept segregated until just prior to application, as is the case with the WO 2010/112106 coating composition. Once all of the components are combined (as when the catalyst (B) is admixed with the coating material containing the binder (A) in making the WO 2010/112106 coating composition) the crosslinking reaction proceeds, increasing viscosity until the viscosity reaches a point where the coating composition can no longer be applied. Any unused material at that point must be discarded. This span of time between combining all of the components and when the viscosity becomes too high for proper application is termed the “pot-life” of the coating composition. It has long been accepted that compositions that are sufficiently reactive to cure at ambient temperatures or in low-temperature ovens (e.g., at 60° C.) to be tack-free after a reasonable time interval (e.g., in an hour) must be formulated as two-component or multi-component coatings in which one or more ingredients are segregated from the remaining coating material until just prior to use. In contrast, one-component curable coating compositions in which all ingredients are combined in a storage-stable package have required high heat or other high energy input, such as actinic radiation, to bring about cure of applied coating layers in a reasonable period of time.
Nakahata et al., U.S. Pat. No. 5,408,001 discloses a three-component resin composition comprising a hydroxyl group-containing compound containing fluorine, an epoxy group-containing compound, and a silanol or hydrolyzable silane group-containing compound. The Nakahata patent also discloses two component resin compositions in which one component has one kind of the groups and the second component has both of the other two kinds of groups. A metal chelate compound is used as a curing catalyst. The composition is reported to be storage stable and capable of curing at room temperature in 8 hours to 7 days or heated to 40° to 100° C. in 5 minutes to 3 hours.